1. Field of the Invention
The present invention relates to a vehicle suspension system for a steerable wheel and, in particular, to a vehicle suspension system for a steerable wheel which can enhance a free layout degree by making it easy to provide an imaginary kingpin axis, and enable cambers thereof to change optimally.
2. Description of Related Art
In general, a vehicle suspension system for a steerable wheel connects an axle and a vehicle body to each other, and absorbs vibrations and impacts from a road surface while running, thereby obtaining safety in a vehicle and an improved ride comfort.
To absorb impacts, a vehicle suspension system should be flexibly connected in a vertical direction, and to endure driving force, braking force and centrifugal force generated at a wheel during a vehicle's turning, a vehicle suspension should be connected firmly in a horizontal direction.
The vehicle suspension system is classified structurally as an axle integral suspension system integrated with a shaft and an independent suspension system. While an axle integral suspension system is applied to large-sized vehicles such as buses, trucks and rear axles of passenger cars, an independent suspension system is applied mainly to an axle of a passenger car. To improve ride comfort and running safety, an independent suspension is bisected to act independently.
Among these suspension systems, the present invention relates to an independent suspension system.
There are many kinds of suspension systems in independent suspension systems. As a suspension system applied to a steerable wheel, Macpherson type and Wishbone type suspensions are widely applied.
A vehicle suspension system for a steerable wheel is designed to control a position of a wheel with respect to the vehicle body to obtain a better positioning in a vehicle operation as well as absorb vibrations or impacts. The axle is thereby prevented from directly transmitting impact or vibration from a road surface to the vehicle body, so that optimal handling safety and running safety can be obtained.
The front wheel is mounted to be changeable in its direction from right to left or from left to right, centering the kingpin, and is also mounted with a geometrical angle to meet front suspension requirements.
Mounting the front wheel with the geometrical angle is called wheel alignment. The wheel alignment is determined by several elements, but the optimal operation of the front wheel is achieved by the supplemental operation of the elements with respect to each other.
A kingpin inclination among the elements reduces a handling force of a steering wheel with a camber, absorbs any impact generated from the vehicle motion and then increases restitution force of the steering wheel. The turning safety of the straight ahead position of the vehicle and the handling safety in a vehicle's turning position are thereby obtained.
The kingpin inclination is such that the kingpin is mounted with its central line lying at a predetermined angle with respect to the vertical line when the vehicle is viewed from the front.
An interval between the central line of the kingpin and a central line of the wheel is called offset. The offset is generally characterized as an offset at the wheel center and an offset at the ground.
The offset at the wheel center has an effect on the straight ahead characteristics of the vehicle when driving force and an engine brake are applied to the wheel.
The offset at the ground has an effect on the handling safety when the vehicle brakes and turns. If the offset at the ground is decreased, the sensitivity with respect to the steering is decreased, while the handling safety is increased when the vehicle brakes and turns.
There is no variation in a camber during ordinary vibration, however, the camber must be changed into a negative (-) valve during a bump, to ensure the running safety of the straight ahead position and the cornering safety.
Considering the above, the conventional suspension system is described in detail hereinafter.
FIG. 4A illustrates a general Macpherson type suspension system including a strut arm 73 formed integrally with a steering knuckle 71, uniting a shock absorber 72 and a spring, a lower arm 74, and a ball joint 75.
This suspension system has some advantages of simple structure, a small spring, light mass, and a small effective volume of an engine room. But in order to have the kingpin offset (a) little or minus, the upper supporting point 76 of the strut arm 73 should be displaced toward the engine room, or the wheel side end of the lower control arm 74 connected to the ball joint 75 should be displaced outside.
However, if the upper supporting point 76 of the strut arm 73 is displaced toward the engine room, the effective volume of the engine room is reduced and the kingpin angle (.alpha.) becomes excessively large only to have a bad effect on cornering safety of a vehicle.
If the wheel side end of the lower control arm 74 connected to the ball joint 75 is displaced outside, it is actually impossible to reduce the kingpin offset (.alpha.) because it will interfere with a brake disk attached to a wheel 77.
FIG. 4B illustrates a general Wishbone type suspension system which comprises upper and lower control arms 81, 82, a steering knuckle 83, a spring assembly 85 including a shock absorber 84, and ball joints 86, 87 connecting the upper and lower control arms 81, 82 to the steering knuckle 83.
To adjust the kingpin offset (.alpha.), a vehicle body side connecting point 88 of the upper control arm 81 should be displaced toward the engine room, or the ball joint 87 of the lower control am 82 should be displaced outside.
In a Wishbone type suspension system, however, as well as a Macpherson type suspension system, if the vehicle body side connecting point 88 of the upper control arm 81 is displaced toward the engine room, the effective volume of an engine room is reduced and the kingpin angle (.alpha.) becomes excessively large to adversely affect cornering safety of a vehicle, and if the ball joint 87 of the lower control am 82 is displaced outside, it is actually impossible to reduce the kingpin offset (a) because it will interfere with a brake disk attached to a wheel 89.